.\" $OpenBSD: atomic_sub_int.9,v 1.6 2014/07/23 08:07:35 guenther Exp $
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.\" Copyright (c) 2014 David Gwynne <dlg@openbsd.org>
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.Dd $Mdocdate: July 23 2014 $
.Dt ATOMIC_SUB_INT 9
.Os
.Sh NAME
.Nm atomic_sub_int ,
.Nm atomic_sub_int_nv ,
.Nm atomic_sub_long ,
.Nm atomic_sub_long_nv
.Nd atomic subtraction operations
.Sh SYNOPSIS
.In sys/atomic.h
.Ft void
.Fn atomic_sub_int "volatile unsigned int *p" "unsigned int v"
.Ft unsigned int
.Fn atomic_sub_int_nv "volatile unsigned int *p" "unsigned int v"
.Ft void
.Fn atomic_sub_long "volatile unsigned long *p" "unsigned long v"
.Ft unsigned long
.Fn atomic_sub_long_nv "volatile unsigned long *p" "unsigned long v"
.Sh DESCRIPTION
The atomic_sub set of functions provide an interface for atomically
performing sub and sub-and-fetch operations with respect to interrupts
and multiple processors in the system.
.Pp
The value referenced by the pointer
.Fa p
is decremented by the value
.Fa v .
.Sh CONTEXT
.Fn atomic_sub_int ,
.Fn atomic_sub_int_nv ,
.Fn atomic_sub_long ,
and
.Fn atomic_sub_long_nv
can all be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Nm atomic_sub_int
and
.Nm atomic_sub_long
perform the subtraction without returning any knowledge of the value at
.Fa p .
.Pp
.Nm atomic_sub_int_nv
and
.Nm atomic_sub_long_nv
return the value at
.Fa p
after the subtraction was performed.
.Sh SEE ALSO
.Xr atomic_add_int 9 ,
.Xr atomic_dec_int 9
.Sh HISTORY
The atomic_sub functions first appeared in
.Ox 5.5 .
